The new findings, which appear in the Aug. 25 issue of Neurology, may give more evidence of the connection between diabetes and Alzheimer's disease.

In insulin resistance, the hormone insulin, produced by the pancreas, becomes less effective in lowering blood sugar. People with insulin resistance are at risk for developing type 2 diabetes.

"Type 2 diabetes and Alzheimer's disease are two epidemics growing at alarming levels around the world," says study researcher Kensuke Sasaki, MD, PhD, with Kyushu University in Fukuoka, Japan, in a news release. "With the rising obesity rates and the fact that obesity is related to the rise in type 2 diabetes, these results are very concerning."

Checking for Signs of Alzheimer's

In the new study, 135 Japanese men and women underwent diabetes screening tests in 1988 and were followed for up to 15 years for signs of Alzheimer's disease. Overall, 16% showed signs of clinical Alzheimer's disease before they died; 65% of people in the study also showed evidence of plaques in their autopsied brains after death.

People who had abnormal results on their blood sugar tests were more likely to have plaques in their brain, the study shows. This relationship was more pronounced among people who also had a form of the ApoE gene that's been linked to a higher risk of developing Alzheimer's disease.

There was no link between insulin resistance and type 2 diabetes and risk for developing brain tangles, another brain abnormality seen with Alzheimer's disease, the study shows.

"Further studies are needed to determine if insulin resistance is a cause of the development of these plaques," Sasaki says. If it is,"it's possible that by controlling or preventing diabetes, we might also be helping to prevent Alzheimer's disease."

The new study "supports the hypothesis that insulin resistance and type 2 diabetes is causally related to a higher risk of dementia including Alzheimer's disease," writes Jose A. Luchsinger, MD, MPH, in an accompanying editorial.

More studies are needed to figure out precisely how the conditions are connected, he writes.

"This is urgent considering that over half of the U.S. population in the age group most at risk for cognitive impairment has prediabetes or type 2 diabetes," he writes.

Some current trials are looking at how available insulin-sensitizing drugs affect cognitive impairment.